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Novel Antitubercular 6‑Dialkylaminopyrimidine Carboxamides from Phenotypic Whole-Cell High Throughput Screening of a SoftFocus Library: Structure–Activity Relationship and Target Identification Studies

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posted on 17.11.2017, 00:00 by Colin R. Wilson, Richard K. Gessner, Atica Moosa, Ronnett Seldon, Digby F. Warner, Valerie Mizrahi, Candice Soares de Melo, Sandile B. Simelane, Aloysius Nchinda, Efrem Abay, Dale Taylor, Mathew Njoroge, Christel Brunschwig, Nina Lawrence, Helena I. M. Boshoff, Clifton E. Barry, Frederick A. Sirgel, Paul van Helden, C. John Harris, Richard Gordon, Sonja Ghidelli-Disse, Hannah Pflaumer, Markus Boesche, Gerard Drewes, Olalla Sanz, Gracia Santos, Maria José Rebollo-Lopez, Beatriz Urones, Carolyn Selenski, Maria Jose Lafuente-Monasterio, Matthew Axtman, Joël Lelièvre, Lluis Ballell, Rudolf Mueller, Leslie J. Street, Sandeep R. Ghorpade, Kelly Chibale
A BioFocus DPI SoftFocus library of ∼35 000 compounds was screened against Mycobacterium tuberculosis (Mtb) in order to identify novel hits with antitubercular activity. The hits were evaluated in biology triage assays to exclude compounds suggested to function via frequently encountered promiscuous mechanisms of action including inhibition of the QcrB subunit of the cytochrome bc1 complex, disruption of cell–wall homeostasis, and DNA damage. Among the hits that passed this screening cascade, a 6-dialkylamino­pyrimidine carboxamide series was prioritized for hit to lead optimization. Compounds from this series were active against clinical Mtb strains, while no cross-resistance to conventional antituberculosis drugs was observed. This suggested a novel mechanism of action, which was confirmed by chemoproteomic analysis leading to the identification of BCG_3193 and BCG_3827 as putative targets of the series with unknown function. Initial structure–activity relationship studies have resulted in compounds with moderate to potent antitubercular activity and improved physicochemical properties.